Drug delivery can be provided by silicon-based multilayered drug delivery flow devices fabricated using a conventional microfabrication process, such as to produce a nanopore membrane for continuous passive drug release to maintain a constant drug concentration in a patient's bloodstream throughout the delivery period. Based on known silicon microfabrication technology, including photolithography and reactive ion etching (RIE), the dimensions of the nanochannel areas, as well as microchannel areas, can be well controlled, thus providing a steady, constant drug release rate over an extended time period. These known multilayered nanochannel structures extend the limit of release rate range over a single-layer nanochannel system, and allow a wide range of pre-defined porosity to achieve essentially any desired drug release rate using any desired nanochannel size. The nanochannel length can generally be reduced to the nanofabrication limit of the process, i.e., 10 s of nms.
A conventional nanochannel drug delivery system membrane comprises a sandwich including a thin top layer, horizontal nanochannels, and a thicker bottom wafer (or chip). The nanochannel thickness controls the rate of drug release. The thin top layer houses an array of nanochannels that provides the inlet port for diffusing drug molecules. The top layer functions as a lid for the nanochannels by providing the nanochannels a top surface. The nanochannels may be fabricated by a sacrificial layer technique to obtain smooth surfaces and well controlled dimensions.
Issues with materials inside the human body include rejection by the body, causing basically an infection, where the material acts as a foreign agent. A second issue arises when the body can dissolve the material. One problem with conventional silicon-based drug-delivery devices is that silicon tends to dissolve in the body, and thus can lead to adverse effects. Silicon-based drug delivery devices must thus generally be protected (coated) by body-friendly non-silicon layers such as silicon nitride or tungsten, which adds steps to the process and raises the cost of the device.